Update git submodules
- Update skins/MinervaNeue from branch 'REL1_39' to 7d8086a6debf0e946defa41ed2426fc1831f1882
- Merge "build: Update MediaWiki requirement to 1.39.0" into REL1_39
- build: Update MediaWiki requirement to 1.39.0
Change-Id: Ia9e27c29c4242de0ef172a32e15746f7142f7572